1. Field of the Invention
The present invention is directed to a method of producing composite optical elements and more particularly to a high speed production method in producing composite elements that can be cured and released from a mold in a short period of time.
2. Description of Background
This invention relates to a method for producing composite optical elements comprised of glass and an organic polymer material. Heretofore, many optical elements such as filters and lenses have been made solely of glass materials. This is because glass is available in a number of different types, glass products can be provided with different refraction powers, high precision can be achieved with glass in the finishing of planar and spherical surfaces and, except for its brittleness, glass is highly durable, to mention but a few reasons. Notwithstanding the broad utility of glass materials, the necessary finishing of such materials is still performed by grinding and polishing and this generally requires a long process time and, hence, high costs of production.
Under these circumstances, optical elements of clear organic polymer materials (plastics) have recently come into common use. With organic polymer materials, the grinding and polishing operations may be omitted and, if suitable processing techniques be selected, those materials lend themselves well to high production. However, up to the present time, only a few types of organic polymer materials have been found to be fully serviceable as optical elements and, with these materials, it has been difficult to obtain the desired refraction powers. Organic polymers are inferior to glass in physical and chemical properties, and especially because their thermal dimensional expansions and thermal changes in refraction powers are considerable, these materials have the disadvantage that, during processing, internal strains and sink-marks are often produced.
To compensate for the above disadvantages of both glass and organic high polymer materials, composite optical elements comprised of a combination of glass and a high polymer have recently been proposed. Such a composite optical element consists of a substrate of glass and a thin layer of a high polymer formed on the substrate. While this product still requires some polishing of the glass substrate surface to close tolerances, the formation of a thin layer of organic high polymer material on the substrate enables one to obtain an optical element of the final desired shape and permits a considerable simplification of the finishing operation. Since the organic polymer segment of the composite optical element is in the shape of a thin layer, the thermal expansion and the thermal change in refraction power are small, and hence, strains and sink-marks are less liable to be present in the final product.
For the production of such a composite optical element, particularly an optical spherical surface, Japanese Patent Laid-Open Publication No. 52/25651 of Feb. 25, 1977 proposed a method in which a photopolymerizable adhesive composition is used as the organic high polymer material. While this method is advantageous in that the polymerization of the photopolymerizable adhesive composition is completed in a short time, this advantage is offset by the disadvantage, that in order to prevent adhesion of the composition to the mold, it requires a complicated sequence of steps, namely the step of applying a mold release agent such as silver to the mold surface by vapor deposition, the step of releasing the composition from the mold and, the step of dissolving the mold release agent to leave the desired optical spherical surface. In other words, the short time for polymerization does not necessarily result in a short overall processing time.